ELECTRONICS FOR YOU ❚ JULY 2001 CIRCUIT IDEAS H ere is a simple telephone ring tone generator circuit designed using only a few components. It produces simulated telephone ring tone and needs only DC voltage (4.5V DC to 12V DC). One may use this circuit in or- dinary intercom or phone-type intercom. The sound is quite loud when this circuit is operated on +12V DC power supply. However, the volume of ring sound is ad- justable. The commonly available 14-stage bi- nary ripple counter with built-in oscillator (CMOS IC CD4060B) is used to gen- erate three types of pulses, which are available from pin 1 (O 11 ), pin 3 (O 13 ), and pin 14 (O 7 ), respectively. Preset VR1 is adjusted to obtain 0.3125Hz pulses (1.6- second ‘low’ followed by 1.6-second ‘high’) at pin 3 of IC1. At the same time, pulses available from pin 1 will be of 1.25 Hz (0.4-second ‘low’, 0.4-second ‘high’) and 20 Hz at pin 14. The three output pins of IC1 are connected to base terminals of transistors T1, T2, and T3 through resis- tors R1, R2, and R3, respectively. Transistors T1 through T3 are cas- caded in such a way that the positive voltage available at the emitter of transistor T1 is extended to the collector of transistor T3 when the outputs of all the three stages are low. As a result, transistors T1 through T3 are forward biased for 0.4, 1.6, and 0.025 seconds, respectively and reverse biased for similar durations. Using a built-in oscillator-type piezo- buzzer produces around 1kHz tone. In this circuit, the piezo-buzzer is turned ‘on’ and ‘off’ at 20 Hz for ring tone sound by transistor T3. 20Hz pulses are available at the collector of transistor T3 for 0.4-second duration. After a time interval of 0.4 second, 20Hz pulses become again available for an- other 0.4-second duration. This is followed by two seconds of no- sound interval. Thereaf- ter the pulse pattern re- peats itself. Refer the figure that indicates wave- forms available at various points includ- ing the collector of transistor T3. Preset VR2 can be used for adjusting the ampli- tude of the ring tone. K. UDHAYA KUMARAN, VU3GTH SIMPLE TELEPHONE RING TONE GENERATOR SUNIL KUMAR

Simple telephone ring tone generator

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Page 1: Simple telephone ring tone generator

ELECTRONICS FOR YOU� ❚❚❚❚❚ �JULY 2001

C I R C U I T I D E A S

Here is a simple telephone ringtone generator circuit designedusing only a few components. It

produces simulated telephone ring toneand needs only DC voltage (4.5V DC to12V DC). One may use this circuit in or-dinary intercom or phone-type intercom.

The sound is quite loud when this circuitis operated on +12V DC power supply.However, the volume of ring sound is ad-justable.

The commonly available 14-stage bi-nary ripple counter with built-in oscilla-

tor (CMOS IC CD4060B) is used to gen-erate three types of pulses, which areavailable from pin 1 (O11), pin 3 (O13), andpin 14 (O7), respectively. Preset VR1 isadjusted to obtain 0.3125Hz pulses (1.6-second ‘low’ followed by 1.6-second ‘high’)at pin 3 of IC1. At the same time, pulsesavailable from pin 1 will be of 1.25 Hz

(0.4-second ‘low’, 0.4-second ‘high’) and 20Hz at pin 14. The three output pins ofIC1 are connected to base terminals oftransistors T1, T2, and T3 through resis-tors R1, R2, and R3, respectively.

Transistors T1 through T3 are cas-

caded in such a way that the positive volt-age available at the emitter of transistorT1 is extended to the collector of transis-tor T3 when the outputs of all the threestages are low. As a result, transistorsT1 through T3 are forward biased for 0.4,1.6, and 0.025 seconds, respectively andreverse biased for similar durations.

Using a built-in oscillator-type piezo-buzzer produces around 1kHz tone. In thiscircuit, the piezo-buzzer is turned ‘on’ and‘off’ at 20 Hz for ring tone sound by tran-sistor T3. 20Hz pulses are available atthe collector of transistor T3 for 0.4-sec-ond duration. After a time interval of 0.4

second, 20Hzpulses becomeagain avail-able for an-other 0.4-sec-ond duration.This is fol-lowed by twoseconds of no-sound inter-val. Thereaf-ter the pulsepattern re-

peats itself.Refer the figure that indicates wave-

forms available at various points includ-ing the collector of transistor T3. PresetVR2 can be used for adjusting the ampli-tude of the ring tone.

K. UDHAYA KUMARAN, VU3GTH

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�� SUNIL KUMAR